Control of standing and gait using electrical stimulation: Influence of muscle model complexity on control strategy

The human body is a multiple-link, unstable inverted pendulum and remains upright only through central nervous system (CNS) motor control programs acting through neuromuscular system actuators. The control problem is to provide reliable, static balance while standing and dynamic balance and trajectory tracking while walking. This chapter presents three approaches to control standing and gait in paraplegics through functional electrical stimulation. The approaches differ in their requirements for modeling the muscle actuator. The first approach describes a detailed muscle model and presents methods for the rapid experimental parameterization of the model. The second requires a less detailed model and knowledge of model error bounds to design advanced, nonlinear controllers that guarantee stability. The third approach needs no muscle model, because it controls limb trajectories through combining stimulation with an orthosis containing controllable friction brakes at the joints. Future clinical systems may use one or a combination of these approaches to restore useful function.